1. Field of the Invention
The present invention relates to a telescope, and more specifically, to a telescope such as a binocular and a monocle.
2. Description of the Prior Art
When a user of a binocular is emmetropic (has normal vision) or wears glasses or contact lenses, it is unnecessary to adjust the dioptric power of the binocular if it is set to 0. In other cases, however, it is necessary to adjust the dioptric power.
In a general binocular where focusing and dioptric power adjustment are performed by manual operations, focusing is performed by objective lenses in both of the left and right lens barrels. The difference between the left and right dioptric powers is corrected by moving either of the left and right objective lenses (or eyepieces) based on an index, representative of a dioptric power of 0, of a dioptric scale provided at a dioptric power adjusting mechanism. Therefore, in the above-mentioned case, the dioptric power is set to 0 by setting the dioptric power adjusting mechanism at the index representative of a dioptric power of 0.
On the contrary, in a binocular where focusing and dioptric power adjustment are performed by driving a focusing lens included in the objective lens by a motor (e.g. a binocular where automatic focusing is performed), it is necessary to adjust both of the left and right dioptric powers.
For example, according to a prior art disclosed by the present applicant in Japanese Patent Application No. H3-185711, a plurality of dioptric powers manually set by the user can be stored in a memory, so that even if the dioptric power is changed, the focusing lens can be set again at the positions corresponding to the stored dioptric powers. However, unless the user stores a dioptric power of 0 in advance, it is impossible to automatically set the focusing lens to the position corresponding to a dioptric power of 0.
Moreover, in apparatuses as disclosed in Japanese Laid-open Patent Applications Nos. S63-206731 and H3-313355 where the dioptric power is automatically sensed and automatically corrected, it is necessary to provide a sensor. This increases the cost and size. Furthermore, when the user of the binocular has normal vision or wears glasses or contact lenses, since it is unnecessary to adjust the dioptric power, an incorrect dioptric power may be sensed. In view of this, setting the dioptric power to 0 is more desirable than automatically adjusting it to the sensed dioptric power.
According to the above-described binocular where the dioptric power adjustment and focusing are manually performed, firstly, it is impossible to find the position corresponding to a dioptric power of 0 while viewing through the binocular. This is because it is impossible to see the index provided at the dioptric power adjusting mechanism while viewing through the binocular. Secondly, since the accommodation range of the human eye is wide, it requires a skill to correctly adjust the dioptric power to meet the user's own dioptric power without seeing the index. This is because the user loses his or her dioptric power in the course of the dioptric power adjustment. If the user is young, it will be particularly difficult to correctly adjust the dioptric power without the index since his or her eye accommodation range is wider. The use of a binocular without the dioptric power being correctly adjusted causes eye fatigue.
Moreover, in the binocular where focusing and dioptric power adjustment are performed by motor driving, to provide the index for dioptric power adjustment at the dioptric power adjusting mechanism, a mechanism such as a motor for driving the lens and the circuit for electrically detecting the position of the index are necessarily provided in both of the left and right barrels. This increases the cost. Therefore, it is difficult to provide the index in such a binocular.
In the binocular where automatic focusing is performed, since in-focus condition is automatically obtained, the binocular is brought into in-focus condition irrespective of the user's dioptric power. For this reason, even if the user's dioptric power is not 0, the user can get a view which is in focus to some extent.
In this condition, although a slightly out-of-focus image should be gotten intrinsically, in-focus condition is forcibly and unconsciously obtained because of the accommodating capability of the human eye. For this reason, the user, who gets an in-focus view, neglects adjusting the dioptric power. Then, the user will continue the observation with the burden of the eyes, so that the eyes will become fatigued if the observation continues for a long time, which is not desirable. Therefore, it is desirable that the dioptric power adjustment position can be set to 0 before the observation so that the dioptric power is adjusted to the condition suitable for the user.
In an automatic focusing bibocular, it is inconvenient that movable parts for AF are exposed outside. Therefore, it is desirable to provide the movable parts inside the body. Then, the index representative of a dioptric power of 0 cannot be provided, so that it is difficult to make the above-mentioned dioptric power adjustment.